Optimisation of culture conditions to obtain the greatest possible productivity is one of the main aim of recombinant protein production. Even marginal increases in productivity can be significant from an economical point of view. Many commercially relevant proteins are produced recombinantly in host cells. This leads to a need to produce these proteins in an efficient and cost effective manner. Unfortunately, one of the drawback of recombinant protein production is that the conditions in which cell culture is performed usually favors a reduction of cell viability over time, reducing both efficiency and overall productivity.
Perfusion culture, Batch culture and Fed batch culture are the basic methods for culturing animal cells for producing recombinant proteins.
Very often, especially in fed-batch and perfusion methods, inducing agents are added to the culture media to increase production of proteins in cells. These inducers induce the cell to produce more desired product. One such agent is sodium butyrate. However, the drawback of using sodium butyrate in cell culture is that it affects significantly cell viability. For instance Kim et al (2004) have shown that although sodium butyrate was able to increase protein production in recombinant CHO cells in a batch culture, at the end of the production run (after 8 days of culture), cell viability was less than 45%. Repeating the same experiments in perfusion batch culture, the authors noticed that within 6 days of treatment, cell viability was as low as 15%.
Although the use of an inducer can increase protein production, the drawback concerning cell viability has to be considered. Indeed, the use of a well-known inducer, such as sodium butyrate, can be counterproductive after about 5 days in culture, whereas a typical production period is between 12 to 15 days in fed-batch mode and can be up to 40-45 days in perfusion mode.
Because many proteins are recombinantly produced by cells grown in culture for more than 6 days, there is a need for methods allowing increased cell productivity and more efficient production runs, while maintaining acceptable cell viability over a longer time.
Therefore, there remains a need for culture conditions and production methods allowing for increased recombinant protein productivity by maintaining viable cell density, increasing the titre and/or avoiding substantial decrease in cell viability over a production period. The present invention addresses this need by providing methods and compositions for increasing production of recombinant proteins.